What is Nature?
What falls under the concept of nature and what does not? What does the concept include and what does it exclude? The OED defines “nature” as follows: “the phenomena of the physical world collectively, including plants, animals, and the landscape, as opposed to humans or human creations”. The Cambridge Dictionary gives us: “all the animals, plants, rocks, etc. in the world and all the features, forces, and processes that happen or exist independently of people, such as weather, the sea, mountains, the production of young animals or plants, and growth”. Construed as analyses of the concept, or even as descriptions of the common use of the word “nature”, these attempts at definition leave much to be desired. First and most glaring, they exclude human beings from nature: human nature is not taken to be part of nature. This is totally arbitrary and flagrantly pre-Darwinian: didn’t we descend from apes, and aren’t apes part of nature? Even if you think humans contain a divine spark—an immortal soul—you surely accept that some aspects of human nature belong to nature (respiration, digestion). What would Martins think if they visited earth—that those funny-looking featherless bipeds are not part of nature? What then are they a part of? Second, the OED explicitly, and the Cambridge Dictionary implicitly, excludes minds from nature: it is the phenomena of the physical world that are said to constitute nature. So minds are not deemed part of nature, even though the organisms that have them are. How is that defensible? Minds evolved, have a genetic basis, and function to aid survival—all the marks of life on earth: they are surely as much a part of nature as bodies. Third, the creations of humans are declared not to be part of nature either. What does this include? Dwellings, weapons, spoken language, culture, and roads would seem to be creations of humans—are they not parts of nature? Aren’t animal nests, hives, burrows, bowers, webs, and tools part of nature? But if so, why are human artifacts declared external to nature (not to mention footprints and prepared food)? Finally, there is no mention of things traditionally supposed outside of nature, particularly the supernatural. Presumably this is intended by implication, since God, angels, and ghosts are not usually thought of as “phenomena of the physical world”, but the point bears emphasis: the concept of nature is supposed to contrast with what is beyond nature—what transcends it, flouts its laws. Heaven is not a department of nature and God himself is not an inhabitant of nature; part of the meaning of “nature” is that these items are not elements of the entity denoted. Nature is what is not supernatural—what is of the earth, sublunary, tangible, non-miraculous, and perishable.
So can we do better? In fact the concept is difficult to define explicitly, ubiquitous as it is. One might even be tempted to wax family resemblance about it. But I think two points are relatively clear: (a) nature is not supernatural and (b) nature is not fictional. As to (b), fictional worlds don’t belong to the realm of nature: for it is at least a necessary condition of being in nature that the thing in question exists. Horses are in nature but unicorns are out, Shakespeare is in but Hamlet is out. You can’t be a part of nature unless you are real. Of course fiction itself can be part of nature—written texts, oral traditions, inner stories, dreams—but not the things fiction talks about. Putting these two points together, then, we can say that nature is what is real and not supernatural: intuitively, it is what exists here, in this world with us, alongside animals, plants, and rocks. It is not otherworldly or purely imaginary. But this still leaves a lot of latitude and unclarity. Are laws of nature part of nature (e.g. the law of entropy)? What if there is a soul in man and a vital spirit in animals? What if atoms don’t really exist? To these questions I think we should answer as follows. Laws of nature are part of nature, since they are inseparable from it, simply being very general. Even if humans and animals contain a part that is not of nature, they contain parts that are, so they do belong to nature (as well as to something outside of it perhaps). If indeed atoms are fictions, then they do not qualify as inhabitants of nature, since what is fictional is not part of nature. This third point should be emphasized: fictionalism about a class of entities is incompatible with counting them as parts of nature. According to Berkeley, material objects are not a part of nature, since matter is a philosopher’s fiction (though not tables, chairs, etc.). According to positivism, the unobservable entities of physics are “logical fictions” that don’t really exist, so they are not elements of nature. Nature might be composed solely of mental entities with nothing “physical” at all; nature is not by definition coterminous with the physical (whatever exactly that word means). Maybe nature consists entirely of consciousness in the manner of panpsychism. This is a matter of what your metaphysics happens to be not of the very meaning of “nature”. In Berkeley’s system nature consists of ideas in the minds of finite spirits and in the mind of the infinite spirit, with matter deemed fictional. For a materialist nature consists of matter as described by physics, while anything not of this kind lies outside of nature, possibly in an immaterial realm. The concept of nature is strictly neutral between these possibilities. That is why I defined it as what is non-fictional and non-supernatural.
The question that particularly interests me once we have these definitional issues out of the way is this: do logic and mathematics (and also ethics) lie within nature or outside of nature? I have never seen this question discussed, but I think most philosophers would be inclined not to include these domains within nature: for they are too abstract and ethereal (“non-empirical”) to belong with animals, plants, rocks, and landscapes (or even human organisms). Ethics, in particular, is not part of nature, being steeped in things called norms—you can’t derive an “ought” from an “is”, and obligations are not natural entities like hearts, livers, and atoms. Now this decision might be grounded in fictionalism: if you believe that logic, mathematics, and ethics are all about fictional entities, then you won’t be inclined to include them in an inventory of the contents of nature. Nature abhors the non-existent. But that is not the majority view—so the question is where these areas fall according to other views. If we adopt subjectivism or psychologism about logic, mathematics, and ethics, then we assimilate them to the psychological—and then they belong to nature along with other psychological realities. Mathematics becomes a human creation, an artifact of sorts, and so falls within nature alongside other human artifacts, material and mental; and similarly for logic and ethics. The tough case is realism in these three areas: does Platonism or moral realism exclude mathematics, logic, and ethics from nature? I find myself inclined to dispute this—I tend to suppose that numbers and values are part of nature. I already think that nature includes human creations, including art, science, politics, and philosophy—these are all parts of nature, as that notion is properly understood—but I also think that other realities belong there too. They don’t belong with the supernatural (if such there be), despite their distinctive character; they belong with the rest of nature. They are part of what exists without any supernatural backing or miraculous infusion. Nature is what is real and not supernatural—and this description applies to logic, mathematics, and ethics (understood realistically). So the concept of nature has nothing intrinsically to do with the physical (again, whatever that means), nor indeed with the psychological—it includes even what has traditionally been regarded as “non-empirical” (a priori). Norms and numbers are thus as much part of nature as wings and mountains. Where else would you locate them? Not in the fictional world (if you reject fictionalism) and not in the divine world (if you believe in such a thing), so nature seems the natural place to locate them. Why not locate them there—isn’t it just a prejudice to keep them outside of what we call nature? After all, they are closely intertwined with things already admitted to nature—the world of physics, the process of reasoning, and human action—so why insist on extruding them from the world of nature? Why try to make another world for them to live in? If this requires an expansion of the usual assumed extension of the concept, then so be it—we need to expand well beyond the dictionary definitions anyway. Hasn’t human thought already expanded the concept of nature well beyond its initial range by extending it to human and animal minds, so why stop at the logical, mathematical, and ethical? Let them in, you will feel better for it. For the notion of nature has acquired a strongly honorific connotation: it is good to be part of nature—a member of the naturalist’s club—and vaguely disreputable to linger at the gates unable to gain entrance. We need to be more inclusive with the concept of nature, less snooty and hidebound. So I suggest welcoming logic, mathematics, and ethics into the fold—they too can be proud members of the Nature Club (with all the perks attaching). We needn’t refashion them in order to make them eligible; they can come as they are, in all their glorious singularity. You can be as Platonist as you like and still be greeted as a fully paid up member. We can’t let you into the Nature Club if you are a figment or a deity—we have to keep up standards—but logic, mathematics, and ethics are neither, so they can be happily admitted. The expanding circle includes them without strain or solecism. Mother nature has a wide embrace. Perhaps indeed with the passage of time these new members might be taken as exemplars of their class, not only members in good standing but respected and senior representatives of the Nature Club. They might be listed first in the roster of honorable members. Wouldn’t it be splendid if ethics were to become President of the Society of Nature? In the book of nature ethical norms might stand out for their authenticity, their natural claim to the title. If you want to know what nature is, you need look no further than ethics—though other items no doubt belong to nature too (e.g. atoms and squirrels).
There are other terms that vie with “nature” for its inclusive exclusiveness such as “the universe”, “the cosmos”, “Creation”, “the world”, “reality”. To belong to the extension of these terms is a mark of distinction, distancing you from the merely fictional and (dubiously) divine. But we can hope to bring logic, mathematics, and ethics under such umbrella terms along with “nature”, thereby securing them ontological respectability. Norms and numbers are thus constituents of the universe, elements of Creation, inhabitants of the cosmos, creatures of the actual world, as real as anything—yet they are what they are and not another thing. They shouldn’t be left out in the wilderness, shunned even by the fictional and supernatural; they should be accepted as bona fide parts of nature. Let’s not multiply worlds unnecessarily. If it turns out that there is no supernatural world, then there will only be the natural world left (fictional worlds not being real), and that world is capacious enough to include those hitherto excluded members.
 How the editors of the OED would define “physical” in this context is left unclear, and the difficulties are notorious. Is gravity physical (Newton declared it “occult”)? What about parental behavior in animals? Perhaps they merely mean “non-psychological” (not that the concept of the psychological is free of difficulty).
 What applies to numbers applies equally (if not more so) to geometric forms: they too belong to nature, as do space and time. On the other hand, in addition to fictional worlds, nonsense worlds also fail to belong to nature: mome raths and borogroves are not parts of nature, even if non-fictionally meant. Are merely possible worlds part of nature? That’s a tough one, which I leave for homework.
 There seems to be a natural (though regrettable) human tendency to restrict honorific concepts more narrowly than is reasonable—witness the concepts person, right, true, physical, reason, rational, and others. The concept of nature belongs to this list: people have a tendency to restrict it to certain preferred examples or exaggerate certain alleged paradigms (mountains, rivers, pretty birds). When people say they are “nature lovers” this is primarily what they have in mind, so that mathematics, logic, and ethics don’t get a look in. Truly enlightened nature lovers, however, adopt a more inclusive stance.
 Is philosophical ethics part of nature? Is moral realism as a theory part of nature? Is Platonism as a doctrine part of nature? The answer to all three questions is yes, since they are aspects or expressions of human nature (language and belief being part of human nature). Secularism leads naturally to the hegemony of nature. The less real the supernatural seems to you the less likely you will be to compare exceptional cases to it; thus nature swallows up the real in proportion as it replaces the supernatural. In the days when the supernatural seemed everywhere it was easy to assign mathematics, logic, and ethics to a place at least adjacent to the supernatural realm; but once that world was eclipsed these areas needed a new home–and nature seems the natural place to put them. Reality thus merges with nature in a secular age.